This proposal is in response to the BIOBEHAVIORAL PAIN RESEARCH RFA PA 95056. Over the last 2 years we have developed the ability to perform multislice functional magnetic resonance imaging (fMRI) of the human brain, and written extensive software for analyzing such data. With this technology we have also obtained preliminary results showing the feasibility of conducting prospective studies of the pathophysiology of the human brain during chronic pain. We will specifically study patients suffering from Reflex Sympathetic Dystrophy (RSD) type chronic pain. Our results indicate multiple cortical areas active in normal subjects during painful heat stimulation, and show different activation patterns in RSD patients for similar painful stimuli. Since RSD pain can be temporarily blocked by interrupting sympathetic outflow (axillary block), we have compared the brain activations of the RSD patients to painful stimuli before and after sympathetic blocks, and observed large changes. The standard therapy for RSD patients is a series of sympathetic blocks, which in a small subset leads to permanent relief. We will study cortical representation for spontaneous pain, allodynia, and hyperalgesia (pain abnormalities associated with RSD) throughout the course of therapy, to differentiate by brain activation maps between patients with successful vs. failed outcomes. To this end we will study RSD patients who will undergo their therapeutic blocks in the fMRI gantry. Brain responses to painful stimuli applied to the affected and normal body will be measured, before and after sympathetic blocks. These patients' fluctuations in pain will be monitored psychophysically and by a pain log book. A normal population of matched controls will undergo stimuli and brain scans (without sympathetic blocks), and a sub group will be tested psychophysically, similarly to the RSD patients to provide baseline control data. The normal subjects will also be studied for differences in brain activation to phasic, tonic and C- fiber painful stimuli.